When a ready-mixed concrete truck returns to the plant after delivering a load of concrete, there is often unused unhardened concrete left over in the truck drum. This remaining concrete is referred to as returned concrete. Returned concrete is a heavy burden for the ready-mixed concrete industry.
Due to numerous environmental concerns and cost considerations, many methods to handle returned concrete have been proposed. Some methods available to the concrete industry to handle returned concrete include: (1) concrete reclaiming methods, (2) hardened concrete crushing methods, (3) casting of various concrete elements, (4) washout pits, (5) recycling reclaimed concrete treated with accelerators and super-absorbent polymers, and (6) reclaiming of unset/plastic concrete by treating it with a retarder and then later adding an accelerating agent to restore the concrete to a usable state. However, there are many deficiencies and shortcomings with these methods and systems.
One method to address this problem with returned concrete is to reclaim the cement slurry and aggregates. Unfortunately, concrete reclaiming methods have various limitations and constraints that lead to an inefficient and expensive recycling process. The inefficiencies pertain to high-energy consumption, unusable slurry or slurry water, high maintenance costs, and so forth. By way of example, DE Patent No. 3,906,645, issued to Sandau on Sep. 13, 1990, discloses a washing apparatus for returned unset/plastic concrete.
A second method to address this problem with returned concrete is discharging it in a pile, allowing it to harden, and then crushing the concrete into stockpiles. The crushed concrete can then be reused or sold. This method requires a significant investment in equipment and its maintenance to crush the hardened concrete.
A third method to address this problem with returned concrete is to cast various concrete elements. These elements may include mooring blocks, anchor blocks, decorative elements, and so forth. This method requires an investment in reusable forms, space for storing the cast elements, and labor to prepare and strip the formwork. By way of example, U.S. Patent Application Publication No. 2004/0179896A1, filed by Curry et al. and published on Sep. 16, 2004, discloses a concrete receptacle assembly and method to make synthetic riprap from returned concrete.
A fourth method to address this problem with returned concrete is to dilute it with a large amount of water and then to discharge the mixture into a washout pit to prevent the solids from binding. After a waiting period, the excess water is drained from the washout pit. The solids are then removed from the washout pit with heavy machinery and stockpiled for drying. The dried solid material is then landfilled for disposal. This process is expensive, time consuming, and environmentally unsustainable. The heavy machinery required to handle the reclaimed material remaining in the washout pit is subject to mechanical failure due to accumulation of the fine particles generated during the reclaiming process.
A fifth method to address this problem with returned concrete is to reuse unset/plastic concrete by recycling it with accelerators and super-absorbent polymers. By way of example, EP Patent No. 2,468,695, issued to Ferrari on Jun. 27, 2012, discloses a method for recycling reclaimed concrete comprising of the addition of flash setting accelerators and super-absorbent polymers to the residual fresh concrete and blending this mixture until granular material is formed. After the granular material is produced, it is discharged and allowed to harden. An objective of this method is the production of granular materials from residual concrete, which, after curing, can be used as aggregates for concrete. A disadvantage of this method is that the treated cementitious material forms a thick coating around the aggregate particles and the hardened properties of the coating significantly affect the quality of the granular material produced with this process. The amount of accelerator and super-absorbent polymer must be carefully controlled to ensure that the quality of the coating around the granular material is appropriate. The treated material also requires early breakdown to ensure that the coating around the various granular particles do not coalesce. Insufficient breakdown of the treated concrete may result in the formation of large chunks of agglomerated paste and aggregate particles. At the time of reuse, the proportion of the newly formed granular material added to the new concrete must also be done with great care to achieve the desired fresh and hardened concrete properties in the new concrete load.
A sixth method to address this problem with returned concrete is to reclaim unset/plastic concrete by treating it with a retarder and then later adding an accelerating agent to restore the concrete to a usable state. By way of example, U.S. Pat. No. 5,427,617, issued to Bobrowski et al. on Jun. 27, 1995, discloses methods and compositions for reclaiming concrete that allows one to keep the returned concrete unset in the truck mixer overnight and to reuse it the next morning in combination with new concrete, thus preventing the disposal of returned concrete and the production of waste. At the time of reuse, the proportion of residual concrete mixed with the new concrete must be done with care to achieve the desired fresh and hardened concrete properties in the new concrete load. This method does not provide the concrete producer with a method to handle returned concrete for a truck that has returned and needs to discharge the returned concrete to receive another load of concrete as soon as possible, which is most often the case in concrete plants.
Other related utility patents known in the art include the following:
U.S. Pat. No. 4,207,176, issued to Hood on Jun. 10, 1980, discloses the reclamation of unset concrete aggregates.
DE Patent No. 4,143,029, issued to Brenner on Jul. 16, 1992, discloses a waste concrete recycling trough.
DE Patent No. 4,428,415, issued to Sandau on Feb. 15, 1996, discloses a concrete washout unit with large receiver and water supply.
DE Patent Publication No. 19544208, filed by Sandau and published on May 7, 1997, discloses a washing out device for residual material such as concrete.
DE Patent Publication No. 19750296, filed by Sandau and published on Nov. 13, 1997, discloses washing equipment for residual concrete.
WO Patent Publication No. 95/26825, filed by Gleiss and published on Oct. 12, 1995, discloses a residual concrete reprocessing device with a feed screw.
WO Patent Publication No. 2012/084716, filed by Ferrari et al. and published on Jun. 12, 2012, discloses a method for producing aggregates from cement compositions.
U.S. Pat. No. 5,203,919, issued to Bobrowski on Apr. 20, 1993, discloses a method and compositions for stabilizing concrete residues.
DE Patent No. 3,727,907, issued to Bobrowski et al. on Mar. 3, 1988, discloses the recycling of concrete mixtures.
DE Patent Publication No. 19518469, filed by Buss et al. and published on May 3, 2007, discloses a process for the reprocessing of residual concrete.
U.S. Pat. No. 5,396,983, issued to Bozenhardt on Mar. 14, 1995, discloses a cleaning device, particularly for residual concrete reprocessing installations.
U.S. Pat. No. 5,560,495, issued to Brenner on Oct. 1, 1996, discloses a transporter for aggregate produced during reprocessing of residual concrete.
U.S. Pat. No. 5,778,910, issued to Brenner on Jul. 14, 1998, discloses a washing trough for residual concrete.
U.S. Pat. No. 8,167,997, issued to Gray on May 1, 2012, discloses concrete mixtures having stabilized foam admixture.
U.S. Pat. No. 7,670,426, issued to Gray on Mar. 2, 2010, discloses concrete mixtures having aqueous foam admixture.
U.S. Pat. No. 6,375,271, issued to Young, III on Apr. 23, 2002, discloses a controlled foam injection method and means for fragmentation of hard compact rock and concrete.
U.S. Pat. No. 5,951,751, issued to Williams et al. on Sep. 14, 1999, discloses a flowable fill composition and a method of producing and placing a flowable fill material.
U.S. Pat. No. 8,080,105 issued to Krozel et al. on Dec. 20, 2011, discloses methods of manufacturing and using a flowable cement-based material.
Related non-patent literature known in the art includes the following:
There exist various types of low-density, high-porosity concretes made with very high air contents, such as cellular, porous, aerated concrete, and controlled low-strength materials. However, these concrete types are not currently produced for the specific purpose to recycle or treat returned concrete. The objectives of producing low-density, high-porosity concretes are generally to improve the thermal efficiency (improved thermal insulation), improve the fire resistance, improve sound insulation, and reduce the dead load of the structure made with these concretes. Controlled low-strength materials are often used in trench fill and backfill applications where their low strength and high workability are desirable. ACI 523.1R-06 describes the production of cellular concrete and state that its main ingredient is preformed foam, which is created by diluting a liquid foam concentrate with water in predetermined proportions and passing this mixture through a foam generator. ASTM C 869 is a standard specification that covers foaming agents specifically formulated for making preformed foam for use in the production of cellular concrete.
The foregoing patent and other information reflect the state of the art of which the inventor is aware and are tendered with a view toward discharging the inventor's acknowledged duty of candor in disclosing information that may be pertinent to the patentability of the technology described herein. It is respectfully stipulated, however, that the foregoing patent and other information do not teach or render obvious, singly or when considered in combination, the inventor's claimed invention.